How can i make a Glass material that doesn't need any light to shine?
Set the background material to white or light grey in enviroment.
Turn on ambient inclusion in enviroment settings.
Set film to transparent in render settings.

That said, without a directional light you won't get shadows or reflection that make it look like rain.  So you might want to add a light, use an image or movie in the background that the rain could reflect, or set up a light that only throws shadows and place it directly above your rain.

Andrew price did a great tutorial that included rain on the camera, if you have any other issues you might want to check it out on blenderguru.com